WO1998032818A1 - Cooling lubricant emulsion - Google Patents

Abstract

The invention relates to a method for the production of a cooling lubricant emulsion mixed with water, used for metal cutting, whereby a) 2-15 parts by weight of a water-miscible concentrate of a coolling lubricant emulsion are mixed with 98-85 parts by weight of water, so as to obtain a mixture comprising 100 parts by weight, and then b) one disperses 1-14 parts by weight of a non water-miscible native-based cutting oil are dispersed, with strong shearing action into mixture a). The cutting oil is preferably chosen from oxidation-stabilized fatty acid glycerides in the form of triesters with three fatty acids with 14-22 C-atoms per fatty acid, and oxidation-stabilized diesters with two fatty acids with 12-22 C-atoms per fatty acid. The invention further concerns a cooling lubricant emulsion that can be produced by this method, and its use for metal cutting.

Description

 Cooling lubricant emulsion

The invention relates to a new type of cooling lubricant emulsion for metal machining and a method for producing the emulsion.

Cooling lubricants are preparations / mixtures that are used in metal cutting and metal forming to cool and lubricate the tools. The most important machining processes differ in the type of movements that the machined part and tool perform, the geometry of the parts to be manufactured and the machining parameters. A distinction is made, for example, between milling, turning, drilling and grinding as machining operations, as well as rolling, deep drawing and cold extrusion as non-cutting forming.

The common principle of metal-cutting processes is that the cutting edge engages the material and lifts a chip off the surface, creating a new surface. Very high pressures are required to break up the material. The deformation of the chip and the friction that occurs under pressure generate heat that heats up the workpiece, the tool and, above all, the chips. The desired effect of using cooling lubricants is therefore the lowering of the temperature that would otherwise occur in the chips. B. can rise to 1000 ° C, and which has an influence on the dimensional accuracy of the manufactured parts. Another main task of cooling lubricants is to improve the service life of tools that wear out quickly under the influence of high temperatures. The use of a cooling lubricant reduces the roughness of the surfaces, since the lubricant prevents welding of the tool and the workpiece surface and prevents particles from sticking. In addition, the cooling lubricant takes on the task of removing the chips that have formed.

With the new version of DIN 51385 No. 1, a clear designation of the cooling lubricants was created, whereby we speak of non-water-miscible, water-miscible and water-mixed cooling lubricants. According to DIN 51385, the terms "water-mixed" mean the final state of the finished medium (mostly oil-in-water emulsions), but "water-miscible" means the state of the concentrate.

Water-mixed cooling lubricants are produced by the user by mixing a concentrate of the water-miscible cooling lubricant with process water. As a rule, approximately 5% aqueous emulsions are produced. The advantage of this type of cooling lubricant is the good cooling effect, which is based on the thermal properties of the water. Due to the good cooling effect, it is possible to achieve very high working speeds and thus increase the productivity of machines. The lubricating effect of the water-mixed cooling lubricants is sufficient for most machining processes in machining. Another advantage is the low cost that can be achieved by mixing the concentrate with water. The disadvantage of water-mixed cooling lubricants is that they counteract External influences, particularly sensitive to microorganisms, and therefore require more control and care than non-water-miscible cooling lubricants such as cutting oils, grinding oils and forming oils.

The table shows a summary of the requirements for water-miscible and water-mixed cooling lubricants:

- Cooling and lubricating effects

- rust protection

- no attack on non-ferrous metals

- Toxicological harmlessness, especially skin tolerance

- no foaming

- no attack on paints and seals

- emulsion stability

- no sticking or resinification

- good miscibility

- pleasant smell

- clean appearance

- good filterability

- easy disposal.

An overview of the shaping metalworking processes and the aids commonly used for this purpose can be found, for example, in Ullmann's Encyclopaedia of Industrial Chemistry, 5th Ed., Vol. AI 5, 479-486. The spectrum of the forms of supply of the auxiliaries in question ranges from oils to oil-in-water emulsions to aqueous solutions. Non-water-miscible and water-miscible cooling lubricants are often based on mineral oil. The mineral oil qualities used are predominantly combinations of paraffinic, naphthenic and aromatic hydrocarbon compounds. In addition to mineral oils, so-called synthetic lubricants ("synthetic oils") such as polyalphaolefins, polyalkylene glycols and glycol ethers, dialkyl ethers, acetals, natural ester oils and synthetic esters and their derivatives are also important.

In order to meet practical requirements, cooling lubricants must contain various components in addition to the base oil. The most important substance groups are the emulsifiers, anti-corrosion additives, biocides, EP additives, polar additives, anti-fog additives, anti-aging agents, solid lubricant additives and defoamers.

Emulsifiers (e.g. surfactants, petroleum sulfonates, alkali soaps, alkanolamine soaps) stabilize the fine distribution of oil droplets in the aqueous working fluid, which is an oil-in-water emulsion. In terms of quantity, the emulsifiers represent an important group of additives for water-miscible cooling lubricants.

Common anti-corrosion additives (e.g. alkanolamines and their salts, sulfonates, organic boron compounds, fatty acid amides, aminodicarboxylic acids, phosphoric acid esters, thiophosphonic acid esters, dialkyldithiophosphates, mono- and dialkylarylsulfonates, benzotriazoles, polyisobutene succinic acid derivatives) are intended to prevent rusting of metal surfaces. Some corrosion protection additives also have emulsifying properties and are therefore also used as emulsifiers. Biocides (e.g. phenol derivatives, formaldehyde derivatives, Kathon MW) are intended to prevent the growth of bacteria and fungi. EP additives (e.g. sulfurized fats and oils, phosphorus-containing compounds, chloro- ganic connections) are intended to prevent micro-welding between metal surfaces at high pressures and temperatures. Polar additives (e.g. natural fats and oils, synthetic esters) increase the lubrication properties. Anti-aging agents (e.g. organic sulfides, zinc dithiophosphates, aromatic amines) ensure a long service life of the cooling lubricants.

In addition to the cooling effect, the second important function of the cooling lubricants lies in the lubricating effect (see the article by W. Klose: "Cooling lubricants on metal surfaces", messages from the Association of German Email Specialists, 41, Issue 11, pages 138-142 (1993)) The effect of the lubricating components on the formation of surface layers, which have a lower shear strength compared to the base material and thus reduce friction and wear. The spectrum of the surface conditions ranges from adsorptively bound layers through chemical sorption to chemical reaction layers that create a firm bond to the metal surface .

The simplest form of lubricant coating on a surface is adsorptive lubricant layers. They are produced, for example, by mineral oils without special additives. The formation of the adsorption layers can be increased by adding polar active ingredients such as fatty alcohols or fatty esters. In addition to the purely physical adsorption, there is an interaction between the metal surface and the lubricant molecules, which leads to a partial chemisorptive binding of the fatty alcohols or fatty esters.

Typical representatives of chemisorptive lubricant film formers are fatty acids. The hydrophilic carboxyl group is chemically bound to the metal surface by reaction with the metal atoms and the hydrophobic hydrocarbon residue is aligned perpendicular to the surface. The increased adhesive strength of the chemisorptive layer improves this Pressure absorption capacity compared to purely adsorptive layers of lubricant, however, is not sufficient for many cases of metal forming to reduce friction and wear. It is only when EP or AW additives (extreme pressure or anti wear additives) are added that the lubricating performance is sufficiently improved so that even difficult forming processes are possible. These are usually chlorine, phosphorus or sulfur-containing active ingredients. Their effect is based on the formation of chemical reaction layers in the form of metal chlorides, metal phosphates or metal sulfides. For reasons of disposal, there is an attempt today to avoid using chlorine-containing EP additives wherever possible. The reaction layers formed on the metal surface act on the one hand as solid lubricant layers that are constantly removed and renewed during the forming process. On the other hand, they form monomolecular surface films that can attach additional lubricant components.

Water-mixed cooling lubricants are a widely used type of cooling lubricant. In practice, however, different water-mixed cooling lubricants are used in order to meet the different requirements with regard to corrosion protection for the different processed materials, lubricating effect at high working speed, service life and last but not least occupational safety and environmental behavior. Manufacturers of cooling lubricant concentrates therefore have to manufacture many different types, keep them in stock and transport them in small batches. The user may have to discard usable emulsions if a different type of cooling lubricant is required due to changed materials. These processes are expensive and disadvantageous from an environmental point of view.

There is therefore a need for a new type of water-mixed cooling lubricant emulsion that is suitable for a wider range of applications can be used. Such a new type of cooling lubricant is provided by the invention that it is possible to emulsify a non-water-miscible cutting oil on a native basis into a conventional water-mixed cooling lubricant emulsion by using high shear energy and thereby to obtain a stable oil-in-water emulsion . Such a combination with at least two different oil components can be used for a wide range of applications.

The invention therefore relates in a first aspect to a method for producing a cooling lubricant emulsion for metal cutting, in which

a) 2 to 15 parts by weight of a water-miscible concentrate of a cooling lubricant emulsion mixed with 98 to 85 parts by weight of water to obtain a mixture comprising 100 parts by weight, and then b) 1 to 14 parts by weight of a water-immiscible cutting oil on a native basis with strong shear into the Mixture a) dispersed.

It is preferable to use fewer parts by weight of water-immiscible cutting oil than parts by weight of water-miscible concentrate. The proportions of cutting oil to the proportions of water-miscible concentrate are preferably from 10 to 80 to 100 and in particular from 20 to 70 to 100.

The invention is therefore mainly based on dispersing a cutting oil which is not water-miscible on a native basis in a cooling lubricant emulsion which is conventional per se, contrary to the usual teachings in practice. This requires high scissor energy compared to the prior art for producing water-mixed cooling lubricant emulsions. For example to achieve the required shear by stirring with a tooth lock washer. Alternatively, intensive mixers such as an Ultraturrax (number of revolutions 10,000 to 20,000 revolutions per minute) or high-speed rotor-stator systems can be considered. If an Ultraturrax is used, dispersion takes place at 20,000 revolutions per minute for a period of about 1 to about 5 minutes. An alternative to this during operation is to add the cutting oil at a point of high turbulence in the running system. The dispersion is then carried out by the shear forces during the metalworking processes.

The individual components as cooling lubricants or as concentrates for cooling lubricant emulsions are known in the prior art. For example, in sub-step a) an emulsion concentrate can be used, which is composed of about 20 to about 60% by weight of an oil component, preferably ester oil, but also paraffinic or naphthenic mineral oil, which contains lubricating additives if desired, and 0 to 25% by weight Water. The remainder to 100 wt .-% consists of emulsifiers, preferably based on fatty alcohol ethoxylates, corrosion inhibitors, preferably based on alkali carboxylates, amine soaps, ethanolamine soaps and / or ethanolamides, and optionally from other auxiliaries or known for this product group in the prior art Active substances, such as those mentioned in the example concentrates.

Instead of the mineral oil, synthetic oils such as polyolefins can be used. Alternative oil components with increased biodegradability are acetals or dialkyl ethers.

For example, the concentrate of a water-miscible cooling lubricant emulsion used in sub-step a) can be composed of (details in% by weight): Concentrate 1

57% mineral oil

16.5% C 14_20 fatty acid mixture

4.4% potassium hydroxide solution, 45%

5.5% alkylsulfonamidocarboxylic acid

7.0% hexanediol

4.0% petroleum sulfonate

0.4% triazole derivative

3.0% hexahydrazine

0.2% o-phenylphenol

Rest: demineralized water

Concentrate 2

35% mineral oil

7.5% C \ 4_20 fatty acid mixture

11.5% C32-36 di-fatty acid mixture

8.0% C6-9 carboxylic acid mixture

12.5% potassium hydroxide solution, 45%

17.0% ethoxylated fatty alcohols (2-5 ethylene oxide groups)

3.0% hemiacetal

0.3% Na pyrion

Rest: demineralized water Concentrate 3

35.5% mineral oil

6.5% C i4_20 fatty acid mixture

7.0% boric acid

3.0% C6_9 carboxylic acid mixture

11.0% mixture of primary and tertiary alkanolamines

8.5% fatty acid amide

8.5% ethoxylated fatty alcohols (2-5 ethylene oxide groups)

1.0% butyl diglycol

0.2% Na pyrion

Rest: demineralized water

In step b), ester-based oils are used as the water-immiscible cutting oil. Examples of these are native triglycerides or modification products thereof, wax esters and fatty acid esters of monoalkanols having 4 to 12 carbon atoms, for example tallow fatty acid ethylhexyl ester or transesterified rapeseed oil, and fatty acid esters of polyols, in particular trimethylol propane being used as the polyol component. In sub-step b), mixtures of such oils can also be used. The oils can contain additional auxiliaries, in particular EP additives, for example in the form of sulfurized compounds, antioxidants and corrosion inhibitors. The water-immiscible cutting oil is preferably selected from oxidation-stabilized fatty acid glycerides in the form of triesters with three fatty acids with 14 to 22 carbon atoms per fatty acid and oxidation-stabilized diesters with two fatty acids with 12 to 22 carbon atoms per fatty acid. In a further aspect, the invention comprises a ready-to-use water-mixed cooling lubricant emulsion of the oil-in-water type, as can be produced directly by the user by the method described above. The emulsion could also be produced centrally and transported to the individual users. This is uneconomical and ecologically disadvantageous because large amounts of water would have to be transported for this.

For the preparation of the emulsion according to the invention, it is not necessary to carry out steps a) and b) one after the other. Rather, a user of a conventional cooling lubricant emulsion can also practice the present invention by subsequently dispersing a cutting oil into this emulsion, which has already been put into operation, in accordance with sub-step b), as described above.

Furthermore, the invention relates to the use of the cooling lubricant emulsion according to the invention for the machining of metals. Examples of such processing methods are milling, turning, drilling, grinding and lapping.

The emulsions according to the invention can be used for a wide range of applications and lead to better friction wear values than conventional emulsions without the addition of a non-water-miscible cutting oil on a native basis. They also provide improved corrosion protection. In scanning electron microscope images, they act as if

"Two-phase lubricant" with a finely emulsified O / W emulsion and coarsely dispersed cutting oil. The droplet sizes themselves depend on the shear conditions and can therefore fluctuate. The ranges of the droplet sizes overlap, however, so that when determining particle sizes with light scattering methods, for example with a Sympatec Helios Vectra device, usually receives only one distribution maximum. This is preferably in the range between approximately 0.5 and approximately 8 μm, in particular between approximately 1 and approximately 4 μm. The particle size can also be determined by light microscopy or video microscopy.

The ready-to-use water-mixed cooling lubricant emulsion is thus characterized in that it is an oil-in-water emulsion in which more than 95% of the oil particles are smaller than 0.5 μm and in which the cutting oil which is not miscible with water is dispersed in such a way that it is too at least 50% is in the form of particles with a size in the range from 0.5 to 8 μm.

Embodiments

For suitability tests, the concentrates 1 and 3 given above were used as water-miscible concentrates in accordance with sub-step a). The parts by weight of concentrate given in the table below were stirred into so many parts by weight of water (with a water hardness corresponding to 20 ° German hardness) with a glass rod that 100 parts by weight of a conventional cooling lubricant emulsion were formed. Comparative experiments la and lb as well as 3 a and 3 b were carried out with this.

Cooling lubricant emulsions according to the invention were obtained by emulsifying 2 parts by weight of a native ester-based cutting oil into the emulsion according to Ia and part 3a into emulsion 3a. The cutting oil consisted of a mixture of oxidation-stabilized fatty acid glycerides in the form of triesters with three fatty acids with 14 to 22 C atoms per fatty acid and oxidation-stabilized diesters with two fatty acids with 12 to 22 C atoms per fatty acid (P3-multanR 201, Henkel KGaA, Düsseldorf). For this purpose, the cutting oil was added to the water-mixed emulsion and dispersed in with an Ultraturrax for one minute at 20,000 revolutions per minute.

A friction wear test according to Reichert was carried out as a suitability test. This procedure is used to determine the pressure absorption capacity (EP behavior) and to determine the adhesive strength of liquid lubricants. Here, a test roller is adapted to a rotating slip ring by means of a lever system, the lower third of which is immersed in the lubricant to be tested. Before the start of the test, the test roll, which has been cleaned in white spirit, is installed in the swiveling holder. The holder is swung in and clamped. The slip ring remains clamped in the device for several test runs, where it is also cleaned with white spirit after each test run. The test roller is placed on the slip ring by slowly applying the load weight (1.5 kg). The counter on the Reichertwaage is set to 0. When the motor is switched on, the rotating slip ring immersed in the lubricant continuously supplies the contact point with lubricant. When the number 100 is reached on the counter (100 meter friction distance), the test roller is removed from the slip ring. The test roller is removed and the cut mark is measured using a magnifying glass. The ellipse area is calculated as 0.785 * length * width, or is read off using a number table. So many test runs are carried out until the ellipse surfaces of the last 3 test runs do not differ from one another by more than 10%. The smaller the elliptical area, the greater the pressure absorption capacity.

Results:

Claims

claims 1. A method for producing a water-mixed cooling lubricant emulsion for metal cutting, characterized in that a) 2 to 15 parts by weight of a water-miscible concentrate of a cooling lubricant emulsion mixed with 98 to 85 parts by weight of water to obtain a mixture comprising 100 parts by weight, and then b) 1 to 14 parts by weight of a water-immiscible cutting oil on a native basis with strong shear into the Mixture a) dispersed. 2. The method according to claim 1, characterized in that the concentrate of the water-miscible cooling lubricant emulsion in sub-step a) is composed of 20-60% by weight of an oil component which contains lubricating additives if desired, and 0 to 25% by weight of water, the rest 100% by weight of emulsifiers, preferably based on fatty alcohol ethoxylates, corrosion inhibitors, preferably based on alkali metal carboxylates, amine soaps, ethanol amine soaps and / or ethanol amides, and of further auxiliaries or active ingredients. 3. The method according to one or both of claims 1 and 2, characterized in that an ester-based oil is used as the water-immiscible cutting oil in sub-step b), preferably selected from native triglycerides or their modification products, wax esters, fatty acid esters of monoalcohols with 4 up to 12 carbon atoms or fatty acid esters of polyols or mixtures thereof, it being possible for the oil to contain additional auxiliaries, in particular EP additives, antioxidants and corrosion inhibitors. 4. The method according to claim 3, characterized in that the water-immiscible cutting oil is selected from oxidation-stabilized fatty acid glycerides in the form of triesters with three fatty acids with 14 to 22 carbon atoms per fatty acid and oxidation-stabilized diesters with two fatty acids with 12 to 22 C- Atoms per fatty acid 5. The method according to one or more of claims 1 to 4, characterized in that the oil component of the concentrate of the water-miscible cooling lubricant emulsion in sub-step a) is selected from aliphatic or naphthenic mineral oils, ester oils, polyolefins, acetals or dialkyl ethers. 6. The method according to one or more of claims 1 to 5, characterized in that less parts by weight of water-immiscible cutting oil than parts by weight of water-miscible concentrate is used. 7. The method according to claim 6, characterized in that the proportions of cutting oil to the proportions of water-miscible concentrate as 10 to 80 to 100, preferably as 20 to 70 to 100 behave. 8. Water-mixed cooling lubricant emulsion which can be obtained by the process according to one or more of claims 1 to 7. 9. Water-mixed cooling lubricant emulsion according to claim 8, characterized in that it is an oil-in-water emulsion in which more than 95% of the oil particles are smaller than 0.5μm and in which the water-immiscible cutting oil is dispersed in such a way that it is at least 50% in the form of particles with a size in the range from 0.5 to 8 μm. 10. Use of the water-mixed cooling lubricant emulsion according to one or both of claims 8 and 9 for the machining of metals.